Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $65.40   12.783%   $73.7601   $73.76   $73.75   $73.80  
  Purchase #2 $249.56   9.392%   $272.9987   $273.00   $273.00   $273.00  
  Purchase #3 $135.75   3.344%   $140.2895   $140.29   $140.30   $140.30  
  Purchase #4 $238.33   7.610%   $256.4669   $256.47   $256.45   $256.50  
  Purchase #5 $203.71   12.636%   $229.4508   $229.45   $229.45   $229.50  
  Purchase #6 $165.39   3.556%   $171.2713   $171.27   $171.25   $171.30  
  Purchase #7 $211.64   12.144%   $237.3416   $237.34   $237.35   $237.30  
  7 purchase totals = $1,269.78       $1,381.5789   $1,381.58   $1,381.55   $1,381.70